Rapid pyrolysis-based fabrication of high-performance electrochromic WO3 films using polyethylene glycol as a pore-forming agent

Abstract

The development of a simple and efficient method for preparing porous tungsten trioxide (WO₃) electrochromic films using structure-directing agents is highly urgent for their industrialization. To this end, this work presents an efficient approach using rapid co-pyrolysis of polyethylene glycol 400 (PEG-400) and ammonium metatungstate (AMT) to produce mesoporous WO₃ thin films. The findings indicate that the concentration of PEG influences both the wettability of the precursor solution on the FTO substrate and the state of the PEG micelle solution, ultimately leading to WO₃ films with diverse morphologies after the co-pyrolysis of AMT and PEG. The porous structure significantly enhances hydrogen ion intercalation/deintercalation, and thus improves electrochromic properties. The optimized electrochromic films demonstrate a 54.5% optical modulation range at 633 nm, fast switching times (2.8 s for coloration and 1.5 s for bleaching), and a coloration efficiency of 83.2 cm² C⁻¹. In pursuit of broader optical modulation capabilities, we further innovated by developing a multilayer porous film strategy, enabling precise control over thickness through repeated spin-coating/heating cycles. Remarkably, a three-layer configuration achieved an extraordinary optical modulation of up to 87.2%, ranking among the best performances reported in the electrochromic field. This novel methodology paves the way for expedited manufacturing of porous amorphous metal oxide films and positions the enhanced WO₃ film as a highly promising candidate for advanced electrochromic technologies.

Graphical abstract